Welcome Matt. I'd obviously advise check every appliance works and ask for any service history.
Other than that the main thing is damp and rust. The damp would show up as any staining on the internal wall boards and be fairly obvious. The chassis is not zinc plated but the only area that sometimes corrodes is the 20mm square tube that runs around the bottom edge of the van. I'd expect to see nothing more serious than can be rubbed off with your hand if the black paint has worn off. Anything more serious and I would walk away as repairs can be very expensive.

Colin

Ps - I've sent a PM

Hi Matt and welcome to Eribafolk

This is the area to look for rust, as per Colin's post above,

g7p4335-Beware-of-Rust.html

As for the price, it's in the right ball park for that age, perhaps a little steep. Is it a dealership sale or private? Does it come with mover, awning and any other accessories?

Randa

Up until this year I'd have agreed with you about holding there value. My first 3 I sold for more than I paid for them, but not the last one.

Colin

Matt. If it's a private sale do you know how long the current owners have had her and the reason for the sale? It all helps to build the picture. Also, are they known to any Eriba Club or Forum? Nor all owners are but it does help.
Randa

Matt, if the van in question is the one on Gumtree then it could have been a personal import. This is not a problem but would explain a couple of things and raise a key question.
A UK supplied GT specification of the time would usually have come with alloy wheels and an underbed access hatch on the door side. It would also have had the 1200kg axle upgrade and different upholstery. I dot not recall the upholstery colourway shown.
The axle question is something you would need to ask about. If lower than 1200kg you would not really have a decent payload.

Colin